Sief Allah H. and Yasmin H., whose full names were withheld in line with local privacy rules, were followers of the ideology of the Islamic State extremist group, prosecutors said in a statement. They bought thousands of castor beans and developed the toxin ricin to carry out an attack on a crowded public place in Germany. They also turned fireworks into explosives.
Sief Allah H. was arrested in June 2018 in the couple's Cologne apartment, where investigators found about 3,150 castor bean seeds and 84.3 milligrams of ricin along with bomb-making components. His wife was arrested a month later.
The seeds of the castor bean plant are naturally poisonous and can be used to create ricin. The substance kills the body's cells by preventing them from creating protein. A few milligrams are enough to kill an adult if it's eaten, injected or inhaled. Early symptoms include chest pain, breathing difficulties and coughing.
The husband is also charged with two further cases of preparing severe acts of violence, while his wife is accused of having supported him in both cases. Sief Allah H. is also charged with trying to join a foreign terrorist group.
In early 2018, the man also published IS propaganda material online about attacks and suicide bombings, the statement said.
Authorities have said that German security agencies were first warned about the man by foreign intelligence agencies, but the information provided wasn't conclusive enough to act upon. A phone-in tip from the public then helped them confirm their suspicions.